An electronic accessory apparatus for a discharge lamp which includes a control circuit for a switching transistor is described in the referenced U.S. Pat. No. 4,792,887, Bernitz et al, assigned to the assignee of the present application, the disclosure of which is hereby incorporated by reference. The Bernitz patent, especially, describes a switching circuit to control a switching transistor which oscillates between conductive and non-conductive state, to provide operating energy at a suitable voltage to a discharge lamp. The energy is supplied through a diode, so that the discharge lamp receives the energy in form of direct current which has a small alternating component superimposed thereon.
It has been found that when small power high-pressure discharge lamps are coupled to circuits of this type, which use a capacitor at the output of the auxiliary circuit, problems with ignition of the lamp may arise. The capacitor at the output of the circuit provides energy to the lamp during the time when no energy is available directly from the power supply network. In the particular circuit, this is the case when a cross-connected semiconductor is conductive. The capacity value of this capacitor must be selected to be sufficiently large that it can supply current to the discharge lamp with only a small a-c component, derived from the switching frequency of the semiconductor, so that the lamp does not extinguish when no current is being supplied, due to the rectification, typically by a diode, from the oscillating semiconductor. The capacity value of this capacitor must be small enough, however, so that the voltage at the capacitor can rise rapidly enough in view of the switching frequency, and duty cycle of the inverter circuit. Both requirements--sufficient energy supply and sufficient energy storage capacity--can be met by an output capacitor. Upon initial ignition, however, the pulsed, rapid discharge of the relatively small capacitor, which may, for example, have a capacity value in the order of only several micro farads, may cause problems, since the duration of the discharge current from the output capacitor may not be long enough to ensure transition of the high-pressure discharge lamp into a stable arc discharge.